(1) Field of the Invention
The present invention relates to a process for producing an N-vinyllactam, wherein a lactam and acetylene can be reacted at a relatively low pressure using a particular catalyst. N-vinyllactams are an important compound used as a material for production of a polyvinyllactam or a copolymer of N-vinyllactam and other vinyl compound.
(2) Description of the Prior Art
N-vinyllactams have been most typically produced by a two-step process. In the first step, an alkali metal hydroxide such as potassium hydroxide is reacted with a lactam to form a corresponding lactam salt catalyst and, in the second step, a lactam is vinylated with acetylene in the presence of said lactam salt catalyst to produce an intended vinyllactam. In this process, however, water is generated in the first step; the water gives rise to lactam ring opening to produce a by-product, namely potassium 4-aminobutyrate, or induces ring-opening polymerization of lactam to produce a by-product polymer; thus, there had been a destruction of catalyst or waste of lactam.
In order to alleviate above problems, various studies were made. For example, in Japanese Patent Application Kokai (Laid-Open) No. 245578/1996, it is described in the Examples (Table 1) that the water formed in the first step and present in the reaction product between lactam and potassium hydroxide, is reduced to 0.1% or less by distillation. However, in this process, relatively high pressures, i.e. an acetylene partial pressure of 18 bar and a total pressure of 20 bar had to be used as seen in the Test Examples of Table 3.
In the reaction of acetylene, as the acetylene partial pressure is higher, the risk of acetylene decomposition and explosion is higher. That is, use of high acetylene partial pressure in reaction is disadvantageous in view of the safety of reaction and the need of special pressure reactor withstanding the pressure. Thus, the process described in the Japanese Patent Application Kokai (Laid-Open) No. 245578/1996 is not fully satisfactory from the standpoint of the industrial applicability.
Meanwhile, in National Publication of International Patent Application No. 501252/1992 is disclosed a process which comprises reacting a lactam and acetylene in the presence of a particular alcoholate catalyst in a nonaqueous system in one step. This process is superior to the process of the Japanese Patent Application Kokai (Laid-Open) No. 245578/1996, because there is no adverse effect by water and the process consists of only one-step.
This process had a problem as well. That is, the conversion of lactam into vinylation product is not sufficiently high even though a reaction is conducted at a relatively high acetylene partial pressure of 100 psig (7 kg/cm.sup.2), as described in Examples.